The brutal murder of prosecutor Jonathan Luna is as puzzling as any he pursued in his too-brief career

There is nothing quite so heart wrenching and at the same time inspiring as a man who loses his life while protecting those of others. Jonathan Luna had seemed such a man. An assistant U.S. attorney in Baltimore, Luna, 38, had spent weeks on a high-profile prosecution of two violent local heroin dealers. The case went to trial, but last Wednesday the defendants opted to plea bargain. Luna and their lawyers spent the day hashing out a plea to be finalized Thursday morning. Yet when morning arrived, Luna was not in court. Soon the whole nation knew why. Four hours earlier,...